The present invention relates to energy distribution systems in vehicles. The present invention particularly relates to a simplified design which at the same time ensures an improved actuation of an electric machine of the power supply system. In addition, the present invention particularly relates to a power supply system for vehicles, in particular electric and hybrid vehicles.
On-board network topologies in electric and hybrid vehicles have at least one energy storage element for holding available, for example, electrically stored energy as well at least one drive element, such as, e.g., an electric motor or an electric machine as a consumer of the stored energy for driving the vehicle. In this connection, an energy storage element, a high voltage accumulator or, respectively, battery system, is connected to the electric machine using an inverter or a DC-AC converter and is designed to emit a DC voltage. In so doing, the converter converts the DC voltage delivered from the energy storage element into an AC voltage suitable for the operation of the motor element, respectively the electric machine.
FIG. 1 shows a conventional on-board network structure for electric or hybrid vehicles. The inverter or, respectively, DC-AC converter is disposed in the conductive path from the energy storage element 4 to the electric motor or electric machine 6. The power supply system 2 furthermore has a charging device 10 which, on the one hand, is coupled to the power supply system and, on the other hand, is coupled to an external energy source 12, such as, for example, an electric power grid 12. In an exemplary manner, the electric power grid 12 is coupled to the charging device with the use of three phases L1-3. Other connections between the electric power grid 12 and the charging device 10 are conceivable. The charging device 10 is thereby equipped to charge the energy storage element 4 due to the external energy supply 12.
Conventional energy storage elements 4 generally have a variable terminal voltage which is dependent on the charging state and which is also applied to the converter 8 via the internal wiring of the energy storage system 2. FIG. 2 depicts an exemplary profile of the current flow provided by the energy storage element 4 as a function of the terminal voltage of the energy storage element 4. Because the output power of the energy storage element 4, as depicted in FIG. 2, is substantially constantly independent of the terminal voltage, a lower terminal voltage requires a higher current flow and vice versa.
In the case of a directly connected DC-AC converter 8, said converter must therefore be dimensioned in such a way that it is able to process the highest possible as well as the lowest possible voltage and the highest possible current as well as the lowest possible current.
The electrical power which is thereby converted by the DC-AC converter 8 is substantially limited by the current which, independently of the terminal voltage applied, may not exceed a certain value. The converter 8 must therefore be designed to handle this maximum current.
In order to now be able to optimally provide a converter, a DC-DC converter 14 can be provided between the energy storage element 4 and the DC-AC converter 8. As a result, the variable voltage emitted by the energy storage element 4, by way of example in the range of 150 V to 300 V, can be transformed or, respectively converted to a voltage level which is substantially constant, for example 400 V. The DC-AC converter 8 can thus be designed to substantially assume a defined operating working point consisting of current flow and voltage without being designed for a large current range. In other words, by means of the defined voltage in the intermediate circuit between the DC-DC converter 14 and the DC-AC converter 8 due to the substantially constant power output, the associated current flow is also set to a substantially constant value. The DC-AC converter 8 preferably can now be designed for this value, without thereby having to take into account reserves for a possibly raised current with a reduced voltage. The DC-AC converter 8 or inverter therefore operates substantially at constant voltage ratios. This is intended to ensure that the current carrying capacity of the semiconductors in the converter 8 can be cut in half. All input parameters can accordingly be configured to a considerably smaller voltage and current range. As a result, the complexity of design can be reduced and material costs can be saved.
An exemplary implementation of a DC-DC converter is shown in FIG. 4. As illustrated in FIG. 4, the DC-DC converter includes inductors L1-L3 and transistor switches T1-T6. The direct current converter 14 or, respectively, DC-DC converter 14 has exemplarily a design as a multi-phase system and thus constitutes a composite of a plurality of individual voltage converters. Technical advantages, such as, for example, the reduction of voltage and current ripples ensue from such a design.
Such a DC-DC converter 14, used according to FIG. 3, is, however, an additional component in the power supply system of a vehicle, which itself has a certain energy consumption and also, already alone on the basis of the weight thereof, has an increased energy requirement for driving a vehicle. Provision is further conventionally made for a charging device 10 which couples an external energy supply 12 into the power supply system such that the energy storage element 4 can be charged.
If a conventional on-board network (cf. FIG. 1) comprising a DC-DC converter for providing a constant supply voltage to the converter is therefore enhanced (cf. FIG. 3), the number of components and therefore the number of semiconductors and the actuators thereof are increased.